Gas generating composition, use thereof in a gas generator and use of a basic mixed metal nitrate

ABSTRACT

A gas generating composition for a safety device in a vehicle comprises an oxidant which comprises a basic mixed metal nitrate, wherein the basic mixed metal nitrate is based on a basic metal nitrate in which the metal of the basic metal nitrate is partly replaced with at least one further element.The disclosure further states the use of such gas generating composition and of such basic mixed metal nitrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage of International Application No.PCT/EP2021/062940, filed May 17, 2021, the disclosure of which isincorporated herein by reference in its entirety, and which claimedpriority to German Patent Application No. 102020113381.2, filed May 18,2020, the disclosure of which is incorporated herein by reference in itsentirety.

TECHNICAL FIELD

The disclosure relates to a gas generating composition, specifically fora safety device in a vehicle, to the use of such gas generatingcomposition in a gas generator as well as the use of a basic mixed metalnitrate.

BACKGROUND

Gas generating compositions usually require, apart from the fuelscontained, additional oxidants to show an equilibrated oxygen balance.

Common oxidants are specifically basic metal nitrates as described, forexample, in Aguirre et al.: “Simple Route for the Synthesis of CopperHydroxy Salts” (J. Braz. Chem. Soc., Vol. 22(3), 2011, pp. 546-551).

An equilibrated oxygen balance is important, for example, to the use ofairbag modules in the interior of a vehicle. In this case, increasedrequirements apply to the propellant gas generated, as said propellantgas may arrive at the interior and thus at occupants of the vehicle viadischarge openings in the airbag, for example. The thresholds of gascomponents such as CO, NH₃ and NO_(x) required in the specifications ofthe car manufacturers can only be achieved by propellant mixtures havinga substantially equilibrated oxygen balance, however.

Additional requirements to gas generating compositions may be theadjustment of the ballistic behavior, such as the setting of a burningtemperature, a burning rate and/or a slag formation while the gasgenerating composition is decomposing.

SUMMARY

The disclosure describes a gas generating composition that allows theburning properties to be controlled and is suitable for use in safetydevices.

According to the disclosure a gas generating composition is describedfor a safety device, specifically in a vehicle, with an oxidantcomprising a basic mixed metal nitrate, wherein the basic mixed metalnitrate is based on a basic metal nitrate in which the metal of thebasic metal nitrate is partly replaced with at least one furtherelement.

DETAILED DESCRIPTION

In other words, in accordance with the disclosure, not only amacroscopic mixture of different basic metal nitrates is used, but amixed metal nitrate with a mixture of a first metal defining thestructure and at least one further metal and/or partial metal whichpartly replaces the first metal on a molecular basis in the crystalstructure. Thus, according to the disclosure, another option isprovided, apart from the oxidants present in the state of the art, toadapt the burning behavior to an intended application of the gasgenerating composition.

Basic mixed metal nitrates in accordance with the disclosure arespecifically compounds which are represented by the following generalformula (I):

(A_(1-x)B_(x))(NO₃)_(y) .n(A_(1-x)B_(x))(OH)_(z)  (I)

In formula (I):

A s the structure-forming first metal,

B is the at least one further element,

X is the proportion of the at least one further element per formulaunit,

Y is the number of nitrate ions per formula unit,

Z is the number of hydroxide ions per formula unit, and

N is the ratio between nitrate ions and hydroxide ions per formula unit.

The value of x in formula (I) is specifically in the range of0.1≤x≤0.95, or in the range of 0.4≤x≤0.8.

Typical values for n, y and z are in the range from 1 to 4, inparticular from 1 to 3, wherein n, y and z can be selected independentlyof each other in the respective range.

The compounds stated in formula (I) may also be provided as hydrates.

In particular, when the basic mixed metal nitrates decompose, at leastternary mixed oxides can form. Such mixed oxides generally have highermelting temperatures or sublimation temperatures than binary metaloxides having one single metal, or than elementary metals, respectively.Thus, at temperatures occurring when the gas generating compositiondecomposes, the at least ternary mixed oxides are provided as solidswhich can be filtered out of the propellant gas more easily than gasesor liquids. In other words, the use of the basic mixed metal nitrateimproves slag formation when the gas generating composition isconverted.

Also, cost savings can be achieved when the at least one further elementis cheaper than the metal of the basic metal nitrate on which the basicmixed metal nitrate is based.

Basic metal nitrates in accordance with the disclosure are compoundswhich are represented by the following general formula (II), whereinsome compounds may also contain hydrates:

M(NO₃)_(y) .nM(OH)_(z) oder M_(x′)(NO₃)_(y′)(OH)_(z′)  (II)

wherein:

M is a metal,

X is the number of metal atoms per formula unit,

y and y′ each are the number of nitrate ions per formula unit,

z′ is the number of the hydroxide ions per formula unit, and

n is the ratio between nitrate ions and hydroxide ions per formula unit.

Typical values for n, x′, y, y′, z and z′ are in the range from 1 to 4,specifically from 1 to 3, wherein n, x′, y, y′, z and z′ can be selectedindependently of each other in the respective range.

Examples of the compounds of the general formula (II) include thosecontaining as metal M copper, cobalt, zinc, manganese, iron, molybdenum,bismuth or cerium, such as basic copper nitrate (Cu₂(OH)₂NO₃ andCu₃(NO₃)(OH)₅.2H₂O), basic cobalt nitrate (CO₂(NO₃)(OH)₃), basic zincnitrate (Zn₂(NO₃)(OH)₃), basic manganese nitrate (Mn(NO₃)(OH)₂), basiciron nitrate (Fe₄(NO₃)(OH)₁₁.2H₂O), basic molybdenum nitrate, basicbismuth nitrate ([Bi(NO₃)(OH)₂] and basic cerium nitrate[Ce(NO₃)₃(OH).3H₂O].

The basic metal nitrate defining the structure of the basic mixed metalnitrate specifically is a basic transition metal nitrate. The basicmetal nitrate can be basic copper nitrate.

Basic copper nitrate is also known as “bCN” (abbreviated for “basiccopper nitrate”) and can be described by the sum formula Cu₂(OH)₂NO₃.Basic copper nitrate is tested for use in gas generating compositionsfor safety devices and is available all over the world. As a result,known formulations comprising basic copper nitrate can be easilyadjusted by the at least partial replacement of the basic copper nitratewith the basic mixed metal nitrate according to the disclosure.

The at least one further element can be selected from the groupconsisting of alkaline earth metals, transition metals, aluminum andboron. In each case, the at least one further element is different fromthe metal of the basic metal nitrate.

The at least one further element can be zinc.

The use of a zinc-containing basic mixed metal nitrate allows tosuppress a light phenomenon occurring when the gas generatingcomposition is converted, which is also referred to as “flaming”. Whenzinc is used as further element in the basic mixed metal nitrate, zincoxide which is doped, at least partially, with the metal and the furtherelements of the basic mixed metal nitrate, respectively, is formedduring the decomposition of the gas generating composition. Zinc oxideis a semiconductor having a band gap that enables ultraviolet andvisible light to be absorbed. The doping with further elements andmetals, respectively, allows to reduce the size of the band gap,resulting in the emission occurring after absorption to be shifted tothe infrared light range. This applies in particular to the case of thehigh temperatures occurring during decomposition of the gas generatingcomposition by which also a reduction of the band gap may occur which iseven intensified by the further doping. Thus, by shifting the lightemission to the range of the infrared light, a reduction of the lightemission visible to humans during decomposition of the gas generatingcomposition can be achieved. Therefore, a user or vehicle occupant willperceive the activation of the safety device as being less negative.

The basic mixed metal nitrate can be a basic copper zinc nitrate, whichis based on basic copper nitrate and hereinafter shall be designatedwith the abbreviation “bCZN”.

The basic copper zinc nitrate is specifically free of hydrate.

During combustion of basic copper zinc nitrate, copper zinc mixed oxidesare formed the melting temperature or sublimation temperature of whichis higher than that of elementary copper so that improved slag formationoccurs. In addition, the afore-described effect of the at least partialsuppression of a light emission in the visible range can be achievedwhen basic copper zinc nitrate is used.

At the same time, the basic copper zinc nitrate in the gas generatingcomposition still can behave similarly to basic copper nitrate so thatthe burning behavior of the gas generating composition is merelytailored but not basically changed via the selected proportion of zincin the basic copper zinc nitrate. Thus, no expensive new formulations ofknown compositions based on basic copper nitrate are required.

Optionally, in the basic copper zinc nitrate a proportion of the coppercan be replaced with at least one further element.

In the basic mixed metal nitrate, specifically 10 mole percent or moreof the metal in the basic metal nitrate are replaced with the at leastone further element, or 40 mole percent or more.

Furthermore, in the basic mixed metal nitrate, 95 mole percent or lessof the metal can be replaced in the basic metal nitrate with the atleast one further element, or 80 mole percent or less.

The mole percent indications refer particularly to the molar amount ofthe metal in the crystal structure of the basic metal nitrate. A crystalstructure of the basic mixed metal nitrate can correspond to the crystalstructure of the basic metal nitrate. In other words, only insignificantdistortions should occur in the crystal structure as compared to thebasic metal nitrate. In this way, the probability increases that thebasic mixed metal nitrate can be used in known formulations for gasgenerating composition without the formulations having to be furtheradapted.

The at least one further element can be arranged to be stochastically orperiodically distributed in the basic mixed metal nitrate. In otherwords, in the basic mixed metal nitrate, an arbitrary distribution ofthe at least one further element can be provided on the theoreticallattice sites of the metal in the basic metal nitrate. As analternative, domains can be formed in the crystal structure of the basicmixed metal nitrate, in which the at least one further element isarranged. The burning behavior of the basic mixed metal nitrate can befurther tailored by appropriately selecting the distribution of the atleast one further element in the crystal structure.

The basic mixed metal nitrate can be obtained by precipitation of one ormore basic nitrate solutions of the individual elements, specifically ofdifferent metal nitrate solutions. For this purpose, production methodscan be used which are analogous to the methods illustrated in DE 102 96592 B4 for the synthesis of basic metal nitrates. The inventors foundthe stoichiometry and the crystal structure of the precipitating basicmixed metal nitrate is influenced both thermodynamically andkinetically. Thus, adaptation of the basic mixed metal nitrate obtainedcan be influenced via the temperature, the pH value, the concentrationsof the nitrate solutions used and their mutual ratio as well as themixing rate of the nitrate solutions. In particular, the molarproportion of the at least one further element can be precisely adjustedin this way.

The gas generating composition may include, as a fuel, all fuels knownin the state of the art and suited for safety devices. For example, thefuel may be selected from the group consisting of boron, aluminum,silicon, magnesium, iron, titanium, tungsten, copper, carbon, zirconium,alloys of the afore-mentioned elements, nitrotriazolone, nitrocellulose,guanidinium compounds, specifically guanidinium nitrate, nitroguanidineand double salts of said compounds, tetrazoles, aminotetrazoles,dinitramides and/or combinations of the above-mentioned fuels.

The fuel is provided in the gas generating composition in a proportionfrom 5 to 95 percent by weight, or in a proportion from 10 to 90 percentby weight or from 20 to 80 percent by weight, or in a proportion from 35to 65 percent by weight.

The gas generating composition may comprise, apart from the basic mixedmetal nitrate, at least one further oxidant selected from the groupconsisting of nitrates, oxides and/or mixed oxides of the alkalinemetals, alkaline earth metals and transition metals, transition metalnitrate hydroxides, chlorates, perchlorates, ammonium nitrate, sulfates,phosphates, oxalates, dinitramides, peroxides, water, oxygen and/orcombinations thereof. Basically, all allotropes and all isotropicmaterials of the corresponding compounds are also included.

The gas generating composition can contain 10 to 60 weight-% of thebasic mixed metal nitrate and, optionally, of the at least one furtheroxidant.

The proportion of basic mixed metal nitrate and, optionally, of the atleast one further oxidant in the gas generating composition isspecifically selected so that an equilibrated oxygen balance isobtained.

The gas generating composition may additionally comprise 5 weight-% orless of a processing aid, specifically 1 to 5 weight-%, based on thetotal weight of the gas generating composition. Processing aids are,e.g., pressing aids, anti-caking aids and/or sliding aids which in thegiven amount have no substantial effect on the burning rate of thecomposition.

Examples of suitable processing aids are polyethylene glycol, cellulose,methyl cellulose, graphite, wax, metal soaps, such as calcium stearate,magnesium stearate, zinc stearate and/or aluminum stearate, boronnitride, talcum, bentonite, silica and molybdenum sulfide as well as themixtures thereof.

In addition, the gas generating composition according to the disclosuremay contain common burning moderators and/or coolants, for example 10weight-% or less, specifically up to 6 weight-% or 0.1 to 6 weight-%,based on the total weight of the gas generating composition. Theabove-mentioned additives have a stabilizing effect on burning and keepthe combustion temperature low. At the same time, slagging of thecombustion residues is improved, which prevents the residues from beingdusted.

Examples of suitable burning moderators and/or coolants are B₂O₃, Al₂O₃,MgO, TiO₂, SiO₂, Mg(OH)₂, basic magnesium carbonate, CaCO₃ and mixturesthereof.

Further, the gas generating composition may additionally comprise 5weight-% or less of a further additive, specifically 0.1 to 5 weight-%,based on the total weight of the gas generating composition. The furtheradditives serve specifically for improving the ignitability and themechanical properties of the gas generating composition.

The burning temperature of the gas generating composition can range from1700 K to 2300 K.

The disclosure further describes the use of a gas generating compositionof the above-described type in a safety device, specifically for avehicle.

Moreover, the disclosure describes the use of a basic mixed metalnitrate of the above-described type as oxidant in a gas generatingcomposition, specifically in a gas generating composition for safetydevices.

The safety device is arranged, for example, in a vehicle or in a vestor, resp., a protector of a user.

Further advantages and characteristics will result from the followingdescription and the examples in the description.

Exemplary gas generating compositions are listed in Table 1.

TABLE 1 Gas generating compositions according to the disclosureComponent Substance Weight-% fuel GuNi 45 to 55 oxidant bCZN 43 to 53processing aid metal stearates 0 to 3 coolant Al₂O₃ 0 to 3 burningmoderator TiO₂ 0 to 3

The abbreviations used in Table 1 have the following meaning:

GuNi=guanidinium nitrate

bCZN=basic copper-zinc-nitrate (basic mixed metal nitrate)

As metal stearates, a mixture of calcium stearate, magnesium stearate,zinc stearate is used.

The ballistic behavior was carried out based on a test series with threecompositions as stated in Table 2.

To this end, the gas generating compositions were compressed intocylindrical tablets having a diameter of 4 mm and a thickness of 1.3 mm.The oxidant used had a grain size d50 of 6 μm. The zinc content in thebCZN used was 22%.

Subsequently, 10 g of the tablets were weighed in a standard combustionchamber made of steel having a volume of 100 cm³, were ignited via anigniter of the standard combustion chamber, and the pressure curveinside the standard combustion chamber was observed to determine thecombustion rate of the respective tablet. The ballistic test was carriedout at a pressure of 10 MPa or 20 MPa, respectively. Each test wascarried out twice and the combustion rates obtained were averagedarithmetically. It turned out that combustion rates measured with thecompositions according to the disclosure for tablets of the size usedand with oxidant of the grain size used are in a range which is suitablefor gas generating compositions for use in safety devices.

TABLE 2 Composition for ballistic tests. Example bCZN GuNi Additives 1 45.9 weight-% 51.24 weight-% 2.86 weight-% 2  48.5 weight-% 48.64weight-% 2.86 weight-% 3 47.41 weight-% 49.73 weight-% 2.86 weight-%

TABLE 3 Results of the ballistic tests of the examples from Table 2Combustion rate Combustion rate at 10 MPa at 20 MPa Example [mm/s][mm/s] 1 15.2 19.2 2 15.2 19.4 3 14.8 18.8

When, in Example 1, bCZN is completely replaced with bCN having a grainsize d50 of 1 μm, combustion rates of 17.6 mm/s at 10 MPa and of 22.2mm/s at 20 MPa are resulting.

When, in Example 1, bCZN is completely replaced with bCN, which wascoated with one percent of glycerin, having a grain size d50 of 1 μm,combustion rates of 19.5 mm/s at 10 MPa and 24.3 mm/s at 20 MPa areresulting.

1. A gas generating composition for a safety device, specifically in avehicle, with an oxidant comprising a basic mixed metal nitrate, whereinthe basic mixed metal nitrate is based on a basic metal nitrate in whichthe metal of the basic metal nitrate is partly replaced with at leastone further element.
 2. The gas generating composition according toclaim 1, wherein the basic metal nitrate is a basic transition metalnitrate, preferably basic copper nitrate.
 3. The gas generatingcomposition according to claim 1, wherein the at least one furtherelement is selected from a group consisting of alkaline earth metals,transition metals, aluminum and boron.
 4. The gas generating compositionaccording to claim 1, characterized in that wherein the at least onefurther element comprises or is zinc.
 5. The gas generating compositionaccording to claim 1, wherein, in the basic mixed metal nitrate, 10 molepercent or more of the metal in the basic metal nitrate are replacedwith the at least one further element.
 6. The gas generating compositionaccording to claim 1, wherein, in the basic mixed metal nitrate, 95 molepercent or less of the metal in the basic metal nitrate are replacedwith the at least one further element.
 7. The gas generating compositionaccording to claim 1, wherein a crystal structure of the basic mixedmetal nitrate corresponds to a crystal structure of the basic metalnitrate.
 8. The gas generating composition according to claim 1, whereinthe at least one further element is arranged to be distributedstochastically or periodically in the basic mixed metal nitrate. 9.(canceled)
 10. (canceled)
 11. The gas generating composition accordingto claim 1, wherein, in the basic mixed metal nitrate, 40 mole percentor more of the metal in the basic metal nitrate are replaced with the atleast one further element.
 12. The gas generating composition accordingto claim 1, wherein, in the basic mixed metal nitrate, 80 mole percentor less of the metal in the basic metal nitrate are replaced with the atleast one further element.